The use of plunger pumps to produce oil from a well having usable gas pressure is well known. In basic principle, a plunger pump is dropped from the surface through the well casing or tubing and into the oil/gas mixture downhole. A mechanism, typically one operated by hydrostatic pressure, closes a passage in the plunger pump to allow gas pressure to build up beneath the pump. The gas pressure builds to a point where it lifts the pump, and a quantity of oil above the pump, to the surface where the oil is recovered. The gas pressure beneath the pump is relieved to allow the pump to fall downhole again to re-initiate the sequence.
One example of a plunger pump is disclosed in U.S. Pat. No. 4,070,134, issued Jan. 24, 1978 to Gramling. However, this device has not proven reliable in actual use, and a need exists for an improved plunger pump which provides for efficient production of oil, condensate, and de-watering of gas wells, either through casing or tubing. For simplicity, the following discussion will be limited to the plunger pump application in casing, with the understanding that the same principles of operation can be applied to its use in tubing.